Fermentation occurs in fruits, bacteria, yeasts, fungi, as well as in mammalian muscle. Yeasts were discovered to have connection with fermentation as observed by the French chemist, Louis Pasteur. Pasteur originally defined fermentation as respiration without air. However, fermentation does not have to always occur in anaerobic condition. Yeasts still prefer to undergo fermentation to process organic compounds and generate ATP even in the presence of oxygen. However, in mammalian muscles, they turn from oxidative phosphorylation (of cellular respiration) to fermentation when oxygen supply becomes limited, especially during a strenuous activity such as intensive exercising.

Fermentation is believed to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere, and thus would represent a more ancient form of energy production in cells.

Fermentation occurs naturally but humans have used and controlled the process. It is used in the production of alcohol, bread, vinegar, and other food or industrial products:

Fermentation (food) - the conversion of carbohydrates into alcohols or acids under anaerobic conditions used for making certain foods.
Fermentation (wine) – the process of fermentation commonly used in winemaking
Fermentation (beer) – the process of fermentation used in brewing beer
Fermentation (tea) - used in the tea industry for the aerobic treatment of tea leaves to break down certain unwanted chemicals and modify others to develop the flavour of the tea
Ethanol fermentation - a form of anaerobic respiration used primarily by yeasts when oxygen is not present in sufficient quantity for normal cellular respiration
Industrial fermentation, the breakdown and re-assembly of biochemicals for industry, often in aerobic growth conditions

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... with slow growth. Given that aerobic organisms *generally* have faster growth rates because ATP production is greater from respiration than from fermentation, aerobic organisms should grow faster and outcompete the others. ...so yeah, I appreciate the comments, but this is not very helpful :(

... non transformed. my supervisor had told me 2 clues (before he went to conference of microbiology - and he is unreachable) that i have to do batch fermentation and *something* PCR. i didnt know either he's talking about real time PCR or reverse transcriptase PCR. what do you think about the clues? ...